Cotton loves to hold in moisture and not let it go! Then there is always the possibility of the darn thing chaffing you under the arms. Can you find some sort of wicking shirt that will do what you need? I just found some wicking tee-shirts for the DF at Old Navy for eight dollars a piece. He works outside and was complaining about the heat and how much he sweats in tee-shirts. I got him four of these shirts and he lives in them! Good luck in finding something that works for you!
Four wheels move the body, two wheels move the soul.
2010 Kelson custom/Brooks B17 Imperial
2009 Masi/Terry Damselfly
2004 Specialized Dulce Elite/Terry Damselfly
2003 Gary Fisher Tassajara/unknown saddle
1987 Bridgestone 100/Terry Liberator X